According to the United Egg Producers Association figures for year 2000 there were 484,000,000 Egg-type chicks (“layers”) eggs set by hatcheries in the U.S. Using their 90% hatchability rate this would result in the production of 435,600,000 waste eggshells. Broiler production industry figures for 2000 showed that 7,800,000,000 eggs were set and with a hatchability rate of 82% this resulted in slightly over 6 billion waste shells.
In addition, the use of eggs by the processed egg sector (“breaker eggs”) during 2000 totaled approximately 1.7 billion (USDA Egg Products Summary, 2000). Breaker eggs are used as ingredients in other processed foods and various food service operations. For example, the albumen (“egg white”) and egg yolk may be recovered to manufacture liquid egg products of various types. In other instances, the albumen and egg yolk may be dried to form a more shelf-stable product (e.g., powdered eggs). In the latter case, the waste egg shells amassed from such processing are usually subjected to further processing (e.g., such as with a centrifuge) in order to recover residual albumen which adheres to the egg shells, which can be sold to the pet food industry.
Even after processing of the breaker egg waste to remove excess albumin, in the year 2000, egg breaking companies in the U.S., produced approximately 13,000 tons of eggshell waste.
Hatchery waste is more difficult to handle than breaker shell since it consists of (a) shells from the hatched chicks (b) unhatched eggs that contain dead embryos and (c) unhatched eggs that were infertile. The hatchability rate for broiler chicks is about 82% while the hatchability for layers is around 90%. The latter situation reflects fewer infertile and dead embryos. The mixed waste (b) and (c) above from hatcheries is either disposed of at the hatchery's expense or recycled by the hatchery company into a feed supplement. Based on the numbers above, which showed approximately 6.5 billion eggs being produced by the hatchery industry, roughly 50,000 tons of eggshell waste is generated which must be disposed of.
A survey conducted in 1997 in collaboration with the United Egg Producers indicated that almost 50% of U.S. egg processors each generate 1000 to 3000 tons of eggshell waste each year. Among the survey respondents, 26.6% used the egg shell waste as fertilizer, 21.1% used it as a feed ingredient, 26.3% disposed of it in dumps as waste, and 15.8% put it to “other” use(s). Among the respondents identifying disposal costs, almost three-quarters reported disposal costs between $25,000 and $100,000 per year.
In view of the significant disposal costs for what is conventionally a waste product, and additionally, in view of current environmental practicalities which are decreasing the availability of local disposal sites (thereby further increasing disposal cost), it will be readily appreciated that finding a significant use for egg shell waste would have important financial and environmental benefits.
It is well known that the eggshell of the chicken is a biologic composite of organic matrix (membrane) and inorganic mineral (shell). The mineral of the shell is mainly calcitic calcium carbonate. The shell membranes remain non-mineralized throughout the assembly of the eggshell and the development of the embryo (Wyburn et al., 1970, Exp. Physiology 55:213). Between the shell and the membrane is a layer of foci of mineralized matrix called the calcium reserve assembly (CRA). The CRA provides the mobilized calcium for the mineralization of the skeleton of the developing embryo (Diekert et al., 1989, Poultry Science 68:1569). At the apex of each CRA is a region known as the crown The crown is a morphologically distinct structure where function is not clear. It may act to separate the resorbable calcium (CRA) and non-resorbable calcium (shell). External to the crown is the shell proper, which is approximately 250 mm in thickness and contains approximately 5 gm of calcium carbonate (Diekert et al., 1989, Poultry Science 68:1569) It is this part of the shell which acts to physically encase and protect the developing embryo (Arias et al., 1991, Matrix 11:313).
Knowledge of the various eggshell structures was critical in developing procedures for recovering and separating eggshell calcium material from the membrane. With breaker eggs, the CRA is still intact after the breaking process. This material provides a very strong bond between the shell and membrane making the separation of shell and membrane very difficult. In contrast, the waste hatchery shell has essentially no CRA left because the developing embryo absorbs the calcium from the CRA, thus destroying the bond between the membrane and the shell (calcium carbonate). During hatchery shell receiving, the membranes separate from the shell as they move along the chick harvesting belt. This phenomenon contributes to a very simple separation procedure.
Two shell membranes surround the egg of most avian species. A thick outer membrane attached to the shell and a thin inner-membrane. Each of these membranes is composed of a network of fibers. Early studies suggested that collagen was present as indicated by hydroxylysine and the digestion of eggshell membrane by collagenase. The presence of Type I and Type V collagen were established in the membrane by Wong (Wong et al., 1984, Developmental Biology 104:28) and Arias (Arias et al., 1991, Matrix 11:313) Other studies (Leach et al., 1982 Poultry Science 61:2040) showed that a unique protein containing lysine-derived cross links was present. Recent studies have identified, among other constituents, type V and X collagen and proteoglycans (mammillan, a keratan sulfate proteoglycan, and ovoglycan, a dermatan sulfate proteoglycan), whose localization depends on a topographically defined and temporally regulated deposition. (Soledad F. et al., 2001, Matrix Biol. 19:793).
The presence of collagen in the shell membranes is noteworthy because of the increasing demand for collagen. Bovine, and to a lesser extent, human, collagen is becoming relatively common and is used in a variety of applications, especially in the biomedical field. For example, a collagen glue made from human collagen is known for filling corneal wounds. Also, research is ongoing in producing skin and tissue replacement products made from collagen. Type X collagen appears throughout both shell membranes. Recent research has shown that Type X Collagen is responsible for prohibiting mineralization of the shell membranes (Sorensen, J., Podiatry Today 1995) and could play a major role in the prevention and treatment of osteoporosis or in the use of arterial transplants where the major reason for failure is calcification of the transplanted valve.
Unfortunately, the cost of such collagen based products is very high (at least about $1,000 per gram, or about $454,000 per pound), although such costs are considered economically acceptable, at least in medical applications, in view of the overall cost of medical treatment.
In addition, use of bovine collagen raises an issue as to the possible transmission of bovine borne diseases, including e.g. bovine spongiform encephalopathy (commonly known as “mad cow disease”). Although the risk of mad cow disease transmission is currently considered very small in this country, the mere perception of possible risk creates a need for private, well-isolated, and expensive herds.
Another problem with bovine collagen is the risk of autoimmune and allergic reactions caused thereby, since approximately 2% to 3% of the population are allergic in this regard. Although, this would appear to be a small percentage, the problem is likely to increase, as the use of bovine collagen products becomes more common.
In summary, a central issue in waste egg disposal is the fact that it is a mixed waste consisting of organic and inorganic components from which it has been difficult, especially in the case of hatchery waste, to extract products of residual value. Eggshell waste is commonly disposed of at the expense of industry and to the detriment of the environment. If practicable processing and recycling methods were available, the reduction of the waste disposal burden would provide important financial and environmental benefits. All totaled, there is a heretofore theoretical potential to recover from the U.S. egg industry more than 55,000 tons of calcitic calcium carbonate from the shell which can be used as pure calcium supplement source for use as a nutritional supplement product such as pills, fruit drinks, cookies other pastries, dairy products, salad sprinkles, cereal and many other food products. In addition, over 5000 tons of membrane, composed of protein, collagen and other components, is available for recovery and recycling (See Table 1 for comparison of protein from egg membrane and other protein sources).